[ithkuil]

Fwiw gravitational waves were predicted by Einstein himself (Einstein, Albert, Ueber Gravitationswellen, 1918) as a consequence of general relativity.

The core idea is that when you move a mass, its contribution to the spacetime geometry changes, but the effects of the change of the geometry doesn't apply instantaneously to all the universe but instead the change propagates at the speed of light.

So that explains why any sudden movement of a mass creates a "crest" that moves through space at the speed of light.

Furthermore, the sources of fast movement of extremely heavy mass just happen to involve an object that wiggles back and forth in a periodic way because those events involve heavy objects orbiting other heavy objects.

That's the reason we can measure a wave with multiple crests and we can talk about a wave length of the gravitational waves: the wave length of the gravitational waves matches the period of the orbit of the heavy mass.

[HappMacDonald]

s/movement/acceleration/g